During the process of offset or dilitho printing, it is a common occurrence for paper fibres, coating, mineral fillers, etc. to be detached from the paper being printed, and for such foreign material to be deposited on or adhere to the printing surface of the press. While this detachment of paper constituents and their deposition on the press results principally from the combined effects of the passage of the paper through the nip under pressure and the tacky inks employed in such printing, it has a deleterious effect on the press performance as manifested by a decrease in the printing plate life and the quality of the copies produced. Similar deposits and accumulation of paper fibres can be formed on dryer cans or calender rolls. While these deposits may be any or all of the paper components indicated above, they will for convenience' sake, be referred to in the following discussion as lint.
Techniques which are currently used to measure the lint on offset printing presses, in order to test the linting properties of papers, are relatively crude and time-consuming. One such method entails the removal and washing of the whole blanket in order to collect the lint sample. Another method is to utilize a sticky-tape eg. a tape with a pressure-sensitive adhesive and to apply it against the surface of the blanket and cause the superficial lint to adhere to the tape, thereby yielding a subjective indication of the lint deposited. This is often misleading as to the linting propensity of the web since only a part of the lint is collected, and furthermore because the linting propensity is estimated visually. The application of this method is restricted to low lint levels, since individual lint fibres have to be counted by eye, and a high density of lint does not permit an accurate count, due to the presence of fibre clusters. The results obtained by this method often vary with the person making the measurement; and additionally their interpretation is ambiguous. While such procedures have been commonly employed for a long time, no simple and efficient lint sampling technique capable of yielding quantitative and objective results has as yet been evolved.
It is therefore the object of this invention to provide a method and apparatus for collecting representative lint samples for measurement and/or testing.